Control circuit for series motors



If Dec. Z8, 1954 D. l.. PETTl-r 2,698,412

CONTROL CIRCUIT FOR SERIES MOTORS Filed July 26, 1952 www f7 f; z/

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INVENTR. 0771' Refi-If CONTROL CIRCUIT FOR SERIES MOTORS Dorn L. Pettit, Milwaukee, Wis., assignor to Square D Company, Detroit, Mich.,,a corporation of Michigan `ApplicationJuly 26, 1952,`Serial No. 301,149

6 Claims. `(Cl. S18-252) This invention relates'to a control circuit for electric motors; more partlcularly thls invention relates to a .control circuit for an electric motor of the type having :a iield winding in series'with the armature.

'One object of the present invention is the provision of 1an improved control circuit fora series motor in which the electrical energy from the supply is used with high -eiciency Another object of this invention is the provision of an improved control circuit for `an electric motor which will :provide both high torque and high speed conditions.

Another object of this invention is the provision of a lcontrol circuit in accordance with the preceding objects and in which the direction of the rotation of vthe motor may be reversed, `the control Vcircuit providing for substantially eliminating the effect of undesirable residual magnetic effects subsequentito the reversing operation.

Another object of the present invention is the prolvision of a control circuit in accordance with thepreceding objects in which vthe motor'may be smoothly accelerated through a plurality o'f speed positions.

Another object of the present invention is the provision lof a control circuit for a series electric motor which will minimize the'heating'in the motor field during reversing operations.

Another object of the lpresent-invntion is the provision 'of a control circuit in accordance ywith the preceding lobjects which may be readily adapted for use with standard series motors.

Other objects and features of the invention will be readily apparent to those skilledin the art from the specification and appended drawing illustrating certain preferred embodiments in which the ligure is a diagrammatic representation of a control circuit in accordance with thepresent invention in which contacts are represented as rectangular boxes, normally closed switches 4s'hown being represented by showing two of these rec- -tangular boxes in contact with `each other, while normally lopen switches are represented by two of these rectangular boxes spaced apart.

In the figure, there is disclosed a pair of conductors 1 and '2 connected to a source of electrical energy, il- 4lustrated as a battery 3. Disposed 'between the conductors 1 and 2 is an electric motor, 'having an armature and atield winding of two equal sections 4 and 5 in series with the armature, through a plurality of switches F1, F2, R1, R2, 1A0 and 2A0 and `1AC and ZAC. A plurality of resistors `6, `7 and 8 are connected as illustrated `in the figure in circuit with the aforementioned switches and motor. While the field winding is shown in two Aseparate sections (4 and 5), it is obvious that a single field 'winding having a center 4tap thereto could be employed.

Connected to the conductor 2 are/a pair of electromagnetic coils F and R, controlling the directional circuit of `the motor, as 'later described. In series with coil F is a normally closed switch R3 and a normally open push button 9; serially connected with coil R is a Ynormally closed switch F3 and a normally open push button 11. As shown in the ligure, there is also connected to conductor 2 a second pair of electromagnetic coils 1A and 2A which control the amount of resistance in circuit with the motor armature, in a manner to be described 1.16,and .parallelling that Iipart of the circuit :including t United States Patent tion.

2,698,412 Patented Dec. 28, 1954 ice Vswitches 12 and 13 is a switch R4 and a switch F4, vas

.closing upon energization of the coil F, while switches F2 and F3 open upon energization of the coil F. Switches R1, R2, R3 and R4 are operated simultaneously by the coil R, energization of coil R effecting closure of switches R1 and R4 and opening of switches R2 and R3. Energization of electromagnetic coil '1A effects opening of the normally closed contact 1AC and simultaneous closure ot' the normally open contact '1AO. In exactly the same manner, switches 2AO and ZAC are operated by electromagnetic coil 2A.

Superimposed upon the figureis a dotted box containing a tabular record of the condition `of each-of the switches 12 through 16 in the four speed conditions of the electric motor, speed 1 being the low speed condition and speed 4 the highest speed condition. While it is obvious that other means may be employed to Voperate switches 12 through 16 in the sequence illustrated, one means for so operating the switches 12 through 16 is the device described and claimed in the `copending application of.. Earl F. Mekelburg `for Accelerating Master Swith, Serial No. 164,281 tiled May 25, 1950. That application also discloses and claims means for operating these switches with a prdetermined time delay in each speed position, which those skilled in the art will readily recognize as desirable in any motor acceleration circuit.

The operation of the circuit of the present invention will now be described:

With the battery 3 connected to conductors 1 and -2, the operator may eiect energization of the control circuit .by first placing switches 12 through 16 in the condition 'described as sneed 1. Then, by closure of either push button 9 or Y11, the associated electromagnetic coil will lbe energized. Assuming the operator closes'push button yfects `closure of switches F1, F4 and opening of switches F2 and Fa. (It will be seen that opening of switch F. prevents energization of electromagnetic coil R until cnil 'F has been deenergized.) Current will then pass from the battery 3, through switch F1, field windings 4 and S. switch R2, resistors 6 and 7, normally closed switch IAC and through the armature to conductor 2.

After a predetermined period. switches 12 through 16 are placed in the speed 2 condition in which switches Y13, 14 and 15 are closed and switches 12 and 16 are open. It will be seen that current will nass through switch F4 and switch 14 to maintain the coil F in an energized condi- In thisspeed position. electromagnetic cnil l1A is energized `so that the normallv open switch 1AO is'closed and the normally closed switch lAC is onen. Current will then pass through switch F1, windings 4 and 5'. switch R2, resistor 6. normally open contact IAO and normally yclosed contact ZAC, through the armature.

When switches 12 through 16 are in the speed 3 condition. switches 12 and 13 are open and switches 14, 15 and V16 are closed. Energization of electromagnetic coil 2A effects closure of the normally open switch 2AO and opening of the normally closed switch 2AC. Current vwill then pass from `the battery through switch F1, winding 4, normally open switch 2AO, resistor 8. and through the armature to conductor 2. ln this speed condition, while some current will pass through winding 5, switch R2 and resistors 6 and 8 to the armature, the value of resistors 6 and 8 is so chosen that the amount of current flow through winding 5 under these conditions is minimized. t

When switches 12 through 16 are placed in the ,speed 4 condition, this being the high speed position, electromagnetic` coil 1A is deenergized while electromagnetic coil 2A remains energized. Current will then pass from the battery through switch Fr, winding 4, normally open switch 2AO and normally closedswitch `IAC through the armature to the yconductor 2. The amount of current -very small through-the'choiceof resistor values.

When the operator desires to reverse the direction of rotation of the armature, push button 9 must be released to deenergize coil F. The switches will then return to the position indicated in the figure. When switches 12 through 16 are returned to the speed 1 position, closure of push button 11 will effect energization of the electromagnetic coil R. Switches R1 and R4 are then closed and switches R2 and Ra are thereby opened. Current will then pass from the battery 3 through switch R1, winding 5, winding 4, switch F2 and resistors 6 and 7, and normally closed switch 1AC to the armature.

As switches 12 through 16 are moved to the speed 2 position, current, which maintains coil R energized. passes through switch R4 and switch 14, the current which energizes coil 1A passing through switches R4, 14 and 15. The current for the motor then passes from battery 3 through switch R1, winding 5, winding 4, switch F2, resistor 6. normally open switch 1AO and normally closed switch ZAC to the armature.

ln the sneed 3 position, coils 1A and 2A are both energized so that current flows from the battery through switch Ri, winding 5, normally open switch ZAO and resistor 8 to the armature, As indicated earlier, very little current will pass through winding 4 in this condition due to th; choice of resistor values in circuit with the winding In the speed 4 position. coil 1A is deenergized while coil 2A remains energized so that substantially the entire armature current passes through switch R1, winding 5. normal- 1y open switch ZAO. normally closed switch 1AC and the armature to conductor 2.

lt will be seen that the control circuit of the present invention may be used with many standard motors by connecting to the center tap of the series field. Tn addition, in view of the fact that with this circuit during the high speed operation in one direction one-half of the total series windings is used to carry substantially the entire armature current, while in the high speed position as the motor is operated in the opposite direction, the other half of the total series windings is used to carry substantially the entire armature current, the heating'` of the motor field is distributed. The circuit also provides for a smooth transition from each sneed position to the next so that acceleration is gradually accomplished, particular attention being called to the fact that as the circuit passes from the sneed 2 position, in which all field windings are used` to speed 3 position, in which only one-half of the total field windings are used, resistance is exerted in series with the partial windings so that the resulting acceleration is accomplished without sudden iolts. It is also obvious that any adverse residual magnetism in field structure is overcome when the motor is reversed, due to the high density field strength obtained by the use of the entire field winding, as the motor begins to operate in the opposite direction. In addition, the battery life is ertended and the energy thereof efiiciently employed in the control circuit of the present invention, and special attention is called to the fact that the lower voltage drop in the field winding when the motor is operated at full speed. increases the efficiency of the motor on long runs.

While certain preferred embodiments of the invention have been specifically disclosed, it is understood that the invention is not limited thereto. as many variations will be readily apparent to those skilled in the art and the invention is to be given its broadest possible interpretation within the terms of the following claims.

What is claimed is:

l. In a control circuit for an electric motor having an armature and a plurality of field winding portions, means for connecting said field winding portions in series and in series with said armature for starting and low speed operation, means for connecting one portion of said windings in series with said armature in a low resistance circuit for high speed operation in one direction of rotation` and means for connecting a different portion of said winding in series with said armature in a low resistance circuit for high speed operation in the opposite direction of rotation.

2. ln a control circuit for an electric motor having an armature and a plurality of field winding portions, a starting resistance, means for connecting said field winding portions in series and in series with said starting resistance and said armature, means for cutting out at least a portion of said starting resistance as the motor speed increases, a secondary resistance, means for connecting one portion of said winding in series with said secondary resistance and said armature as the motor again increases in speed, means for connecting said one portion of said winding directly in series with said armature for full speed operation of said motor in one direction of rotation and means operative as the motor accelerates in the opposite direction of rotation for connecting a portion of said winding different from said one portion in series with said secondary resistance and armature and with said armature alone as the motor accelerates.

3. In a control circuit for an electric motor having an armature and a pair of field windings, forward and reverse switching means determining the direction of rotation of said motor, said switching means operating regardless of the direction of rotation to connect said field windings in series and in series with the armature for starting and low speed operation, means controlled by said forward switching means for connecting one field winding in series with the armature in a low resistance circuit for high speed operation in the forward direction and means controlled by the reverse switching means for connecting the other field winding in series with the armature in a low resistance circuit for high speed operation in the reverse direction.

4. ln a control circuit for an electric motor having an armature and a pair of field windings, forward and reverse switching means determining the direction of rotation of said motor, said switching means operating regardless of the direction of rotation to connect said field windings in series and in series with the armature for starting and low speed operations, means controlled by said forward switching means for connecting one field winding in series with the armature in a low resistance circuit for high speed operation in the forward direction and means controlled by the reverse switching means for connecting the other field winding in series with the armature in a low resistance circuit for high speed operation in the reverse direction, in both forward and reverse operation the winding not in the low resistance circuit being connected through the armature through a relatively high resistance so that only a relatively minor lcurrent flows therethrough.

5. In a control circuit for an electric motor having an armature and a pair of field windings, forward switching means for said motor and winding, reverse switching means for said motor and Winding, a starting resistance, each of said forward and reverse switching means when actuated connecting said windings in series and in series with said starting resistance and armature for an initial speed step, switching means for cutting out at least a portion of said starting resistance to provide a second speed step, and switching means for connecting one of said field windings in series with said armature in a circuit of substantially no resistance, the winding selected for connection to said armature being determined by whichever of the forward and reverse switching means is operated whereby to alternate the windings utilized for high speed operation of the motor.

6. In a control circuit for an electric motor having an armature and a pair of field windings, forward switching means for said motor and winding, reverse switching means for said motor and winding, a starting resistance, each of said forward and reverse switching means when actuated connecting said windings in series and in series with said starting resistance and armature for an initial speed step, switching means for cutting out at least a portion of said starting resistance to provide a second speed step, an auxiliary resistance, switching means for connecting one of said field windings in series with said armature through said auxiliary resistance, the actuation of whichever of the forward and reverse switching means is operated determining which of the field windings is connected to the armature through said auxiliary resistance, and switching means for cutting out said auxiliary resistance to connect the selected field winding directly in series with the armature.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,155,164 Riley Sept. 28, 1.915 1,387,466 Candee Aug. 16, 192,1 2,399,059 Pell Apr. 23, 1946 2,482,513 Rossignol et al Sept. 20,'1949 

